In the medical field, it is often necessary to couple a length of tubing to a patient's blood vessel so as to dispense fluid into the vessel. Rather than pierce the patient's skin a further time, it is advantageous to use the same tubing for other medical purposes as well. For example, during angiographic procedures and other interventional imaging operations, contrast media is typically injected under high pressure through the tubing to a catheter inserted into an artery to generate a radiographic image of the arterial network or other associated location for diagnostic and treatment purposes. The tubing may also be coupled to a pressure transducer by which to obtain the patient's blood pressure in the artery via the hydrostatic column created within the tubing.
Contrast media injection typically requires extremely high pressures, such as 300 psi, and possibly even exceeding 1000 psi. To achieve such pressures, a manual or power injector syringe is typically used. But blood pressure transducers are very sensitive devices designed for low-pressure environments, such as below 2 psi, thus presenting significant challenges when coupled to the same tubing used for high pressure purposes, such as contrast media injection by way of example. In that regard, if steps are not taken to protect the pressure transducer, it could be damaged.
To prevent such damage, a three-way stopcock with three ports may be used. One port is coupled to the transducer (such as via a further length of tubing which may also couple to a saline source), a second port is coupled to the syringe (either directly or via a still further length of tubing), and the third port is coupled to the tubing going to the patient. The stopcock has a lever that can be rotated back and forth between two positions. In one position, the transducer port is fluidicly coupled to the tubing port and the syringe port is fluidicly uncoupled from both the transducer port and the tubing port. In that position, the pressure transducer can sense pressure in the hydrostatic column of the patient tubing. In the other position, the syringe port is fluidicly coupled to the tubing port and the transducer port is fluidicly uncoupled from both the syringe port and the tubing port. In this other position, the contrast media may be injected. At all times, the transducer and syringe ports are fluidicly uncoupled. As a consequence, the pressure transducer is not exposed to fluid or pressure communication with the high pressure source (i.e., the syringe). Further, during high pressure excursions, such as during a contrast media injection, the pressure transducer is not exposed to the tubing through which the high pressure fluid is being injected.
While a stopcock thus can be used to help prevent damage to the blood pressure transducer, it is not without its drawbacks. A stopcock must be manually manipulated, which can interfere with or slow down the medical diagnostic procedure. Moreover, if the lever is not rotated to the desired position, the injection may not be given when or as desired or a valid blood pressure reading may not be obtained.
Another approach to protecting the transducer from exposure to the high pressure during an injection is an automatic manifold which has a series of valves, actuators and/or pistons that respond to the presence or absence of various pressure or signals to selectively couple the tubing to either the syringe or the transducer. Such manifolds have drawbacks as well, including that they are bulky, have several operating components, and are not well suited to use with manual syringes, for example.